Long Term Evolution (LTE)
Third-generation mobile systems (3G) based on WCDMA radio-access technology are being deployed on a broad scale all around the world. A first step in enhancing or evolving this technology entails introducing High-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, also referred to as High Speed Uplink Packet Access (HSUPA), giving a radio-access technology that is highly competitive.
In order to be prepared for further increasing user demands and to be competitive against new radio access technologies, 3GPP introduced a new mobile communication system which is called Long Term Evolution (LTE). LTE is designed to meet the carrier needs for high speed data and media transport as well as high capacity voice support to the next decade. The ability to provide high bit rates is a key measure for LTE.
The work item (WI) specification on Long-Term Evolution (LTE) called Evolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN) is to be finalized as Release 8 (LTE). The LTE system represents efficient packet-based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. In LTE, scalable multiple transmission bandwidths are specified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieve flexible system deployment using a given spectrum. In the downlink, Orthogonal Frequency Division Multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference (MPI) due to a low symbol rate, the use of a cyclic prefix (CP), and its affinity to different transmission bandwidth arrangements. Single-Carrier Frequency Division Multiple Access (SC-FDMA) based radio access was adopted in the uplink, since provisioning of wide area coverage was prioritized over improvement in the peak data rate considering the restricted transmission power of the user equipment (UE). Many key packet radio access techniques are employed including multiple-input multiple-output (MIMO) channel transmission techniques, and a highly efficient control signaling structure is achieved in LTE.
LTE Architecture
The overall architecture is shown in FIG. 1 and a more detailed representation of the E-UTRAN architecture is given in FIG. 2. The E-UTRAN consists of an eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink Quality of Service (QoS), cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of downlink/uplink user plane packet headers. The eNodeBs are interconnected with each other by means of the X2 interface.
The eNodeBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (SGW) by means of the S1-U. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNodeBs.
Component Carrier Structure in LTE
The downlink component carrier of a 3GPP LTE system is subdivided in the time-frequency domain in so-called sub-frames. In 3GPP LTE each sub-frame is divided into two downlink slots as shown in FIG. 3, wherein the first downlink slot comprises the control channel region (PDCCH region) within the first OFDM symbols. Each sub-frame consists of a give number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), wherein each of OFDM symbol spans over the entire bandwidth of the component carrier. The OFDM symbols thus each consist of a number of modulation symbols transmitted on respective NRBDL×NscRE subcarriers as also shown in FIG. 4.
Assuming a multi-carrier communication system, e.g. employing OFDM, as for example used in 3GPP Long Term Evolution (LTE), the smallest unit of resources that can be assigned by the scheduler is one “resource block”. A physical resource block is defined as NsymbDL consecutive OFDM symbols in the time domain and NscRB consecutive subcarriers in the frequency domain as exemplified in FIG. 4. In 3GPP LTE (Release 8), a physical resource block thus consists of NsymbDL×NscRE resource elements, corresponding to one slot in the time domain and 180 kHz in the frequency domain (for further details on the downlink resource grid, see for example 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, version 8.9.0 or 9.0.0, section 6.2, available at http://www.3gpp.org and incorporated herein by reference).
The term “component carrier” refers to a combination of several resource blocks. In future releases of LTE, the term “component carrier” is no longer used; instead, the terminology is changed to “cell”, which refers to a combination of downlink and optionally uplink resources. The linking between the carrier frequency of the downlink resources and the carrier frequency of the uplink resources is indicated in the system information transmitted on the downlink resources. There is a PCell (Primary Cell) and none or several (e.g. up to four) SCells (Secondary Cells). The terms Cell and component carrier are used in the following interchangeably, since both Scells and Pcells may be seen as a component carrier. This however should not be interpreted to restrict the scope of the invention to a particular Release of the LTE standard.
When carrier aggregation is configured, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the NAS mobility information (e.g. TAI), and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as the Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC).
Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC).
The configured set of serving cells for a UE therefore always consists of one PCell and zero or more SCells:                For each SCell the usage of uplink resources by the UE in addition to the downlink ones is configurable (the number of DL SCCs configured is therefore always larger or equal to the number of UL SCCs and no SCell can be configured for usage of uplink resources only);        From a UE viewpoint, each uplink resource only belongs to one serving cell;        The number of serving cells that can be configured depends on the aggregation capability of the UE;        PCell can only be changed with handover procedure (i.e. with security key change and RACH procedure);        PCell is used for transmission of PUCCH;        Unlike SCells, PCell cannot be de-activated;        NAS information is taken from PCell.        
The reconfiguration, addition and removal of SCells can be performed by RRC. At intra-LTE handover, RRC can also add, remove, or reconfigure SCells for usage with the target PCell. When adding a new SCell, dedicated RRC signalling is used for sending all required system information of the SCell i.e. while in connected mode, UEs need not acquire broadcasted system information from the SCells.
Component Carrier Activation/Deactivation
Essentially a downlink component carrier could be in one of the following three states: non-configured, configured but deactivated, configured and activated. When a downlink component carrier is configured but deactivated, the user equipment does not need to receive the corresponding PDCCH or PDSCH, nor is it required to perform CQI measurements. Conversely, when a downlink component carrier is activated, the user equipment shall be able to receive PDSCH and PDCCH (if present), and is expected to be able to perform CQI measurements. After configuration of component carriers in order to have PDCCH and PDSCH reception on a downlink component carrier, the downlink component carrier needs to be transitioned from configured but deactivated to the activated state.
For user equipment power-saving purposes, it's crucial that additional component carriers can be de-activated and activated in an efficient and fast way. With bursty data-transmission, it is imperative that additional component carriers can be activated and de-activated quickly, such that both the gains of high bit-rates can be utilized, and battery preservation can be supported.
If the UE is configured with one or more SCells, the network may activate and deactivate the configured SCells. It should be noted, that according to current Release 10, the PCell is assumed to be always activated; this is however not necessary for the present invention and might also change in the future. The UE will not monitor the PDCCH of a deactivated SCell and will not receive any downlink assignments or uplink grants associated to a deactivated SCell. Correspondingly, the UE will not transmit on the UL-SCH on a deactivated SCell. The network may activate and deactivate the SCell(s) by sending a Activation/Deactivation MAC control element. The MAC control element usually comprises a message (e.g. a bitmap) with information on the activation status of all (or the configured) component carriers. In other words, every time one or more component carriers are to be activated/deactivated, a message for all (configured) component carriers is transmitted in a MAC control element, with information on the respective desired activation status. In this way, the message does not strictly indicate whether a component carrier's activation status is toggled, but just the desired status after the message.
Furthermore, the UE maintains a sCellDeactivationTimer timer per configured SCell and deactivates the associated SCell upon its expiry. In other words, upon expiry of a pre-determined time after having received download data over a component carrier, the UE deactivates said component carrier. Consequently, the UE can deactivate the SCells independently, as the timer runs per SCell and is also reset per SCell.
The same initial timer value applies to each instance of the sCellDeactivationTimer and is configured by RRC. The configured SCells are initially deactivated upon addition and after a handover.
Channel Quality Reporting
The principle of link adaptation is fundamental to the design of a radio interface which is efficient for packet-switched data traffic. Unlike the early versions of UMTS (Universal Mobile Telecommunication System), which used fast closed-loop power control to support circuit-switched services with a roughly constant data rate, link adaptation in LTE adjusts the transmitted data rate (modulation scheme and channel coding rate) dynamically to match the prevailing radio channel capacity for each user.
For the downlink data transmissions in LTE, the eNodeB typically selects the modulation scheme and code rate (MCS) depending on a prediction of the downlink channel conditions. An important input to this selection process is the Channel State Information (CSI) feedback transmitted by the User Equipment (UE) in the uplink to the eNodeB.
Channel state information is used in a multi-user communication system, such as for example 3GPP LTE to determine the quality of channel resource(s) for one or more users. In general, in response to the CSI feedback the eNodeB can select between QPSK, 16-QAM and 64-QAM schemes and a wide range of code rates. This CSI information may be used to aid in a multi-user scheduling algorithm to assign channel resources to different users, or to adapt link parameters such as modulation scheme, coding rate or transmit power, so as to exploit the assigned channel resources to its fullest potential.
The CSI is reported for every component carrier, and, depending on the reporting mode and bandwidth, for different sets of subbands of the component carrier. A channel resource may be defined as a “resource block” as exemplary illustrated in FIG. 4 where a multi-carrier communication system, e.g. employing OFDM as for example discussed in the LTE work item of 3GPP, is assumed. More generally, it may be assumed that a resource block designates the smallest resource unit on an air interface of a mobile communication that can be assigned by a scheduler. The dimensions of a resource block may be any combination of time (e.g. time slot, sub-frame, frame, etc. for time division multiplex (TDM)), frequency (e.g. subband, carrier frequency, etc. for frequency division multiplex (FDM)), code (e.g. spreading code for code division multiplex (CDM)), antenna (e.g. Multiple Input Multiple Output (MIMO)), etc. depending on the access scheme used in the mobile communication system.
Assuming that the smallest assignable resource unit is a resource block, in the ideal case channel quality information for each and all resource blocks and each and all users should be always available. However, due to constrained capacity of the feedback channel this is most likely not feasible or even impossible. Therefore, reduction or compression techniques are required so as to reduce the channel quality feedback signalling overhead, e.g. by transmitting channel quality information only for a subset of resource blocks for a given user.
In 3GPP LTE, the smallest unit for which channel quality is reported is called a subband, which consists of multiple frequency-adjacent resource blocks.
As described before, user equipments will usually not perform and report CSI measurements on configured but deactivated downlink component carriers but only radio resource management related measurements like RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality). When activating a downlink component carrier, it's important that the eNodeB acquires quickly CSI information for the newly activated component carrier(s) in order to being able to select an appropriate MCS for efficient downlink scheduling. Without CSI information the eNodeB doesn't have knowledge about the user equipment's downlink channel state and would most likely select a too aggressive or too conservative MCS for downlink data transmission, both of which would in turn lead to resource utilization inefficiency due to required retransmissions or unexploited channel capacity.
Channel State Information Feedback elements
Commonly, mobile communication systems define special control signalling that is used to convey the channel quality feedback. In 3GPP LTE, there exist three basic elements which may or may not be given as feedback for the channel quality. These channel quality elements are:                MCSI: Modulation and Coding Scheme Indicator, sometimes referred to as Channel Quality Indicator (CQI) in the LTE specification        PMI: Precoding Matrix Indicator        RI: Rank Indicator        
The MCSI suggests a modulation and coding scheme that should be used for transmission, while the PMI points to a pre-coding matrix/vector that is to be employed for spatial multiplexing and multi-antenna transmission (MIMO) using a transmission matrix rank that is given by the RI. Details about the involved reporting and transmission mechanisms are given in the following specifications to which it is referred for further reading (all documents available at http://www.3gpp.org and incorporated herein by reference):                3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation”, version 10.0.0, particularly sections 6.3.3, 6.3.4,        3GPP TS 36.212, “Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding”, version 10.0.0, particularly sections 5.2.2, 5.2.4, 5.3.3,        3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”, version 10.0.1, particularly sections 7.1.7, and 7.2.        
In 3GPP LTE, not all of the above identified three channel quality elements are reported at any time. The elements being actually reported depend mainly on the configured reporting mode. It should be noted that 3GPP LTE also supports the transmission of two codewords (i.e. two codewords of user data (transport blocks) may be multiplexed to and transmitted in a single sub-frame), so that feedback may be given either for one or two codewords. Some details are provided in the next sections and in Table 1 below for an exemplary scenario using a 20 MHz system bandwidth. It should be noted that this information is based on 3GPP TS 36.213, section 7.2.1 mentioned above.
The individual reporting modes for the aperiodic channel quality feedback are defined in 3GPP LTE as follows:
Reporting Mode 1-2
Contents of this report for transmission modes 1-8:                One set S MCSI value per codeword        One preferred PMI for each subband is selected        In case of transmission modes 4 or 8: One RI value        
Contents of this report for transmission mode 9:                One set S MCSI value per codeword        One first preferred PMI for set S        One preferred PMI for each subband        One RI value        
Reporting Mode 2-0
Contents of this report:                One set S MCSI value        Positions of M selected subbands        One MCSI value for M selected subbands (2 bits differential set S MCSI value, non-negative)        In case of transmission mode 3: One RI value        
Reporting Mode 2-2
Contents of this report for transmission modes 1-8:                One set S MCSI value per codeword        One preferred PMI for set S        Positions of M selected subbands        One MCSI value for M selected subbands per codeword (2 bits differential to set S MCSI value, non-negative)        One preferred PMI for M selected subbands        In case of transmission modes 4 or 8: One RI value        
Contents of this report for transmission mode 9:                One set S MCSI value per codeword        One first preferred PMI for set S        One second preferred PMI for set S        Positions of M selected subbands        One MCSI value for M selected subbands per codeword (2 bits differential to wideband MCSI value, non-negative)        One first preferred PMI for M selected subbands        One second preferred PMI for M selected subbands        In case of transmission modes other than transmission mode 4: One RI value        
Reporting Mode 3-0
Contents of this report:                One set S MCSI value        One MCSI value per subband (2 bits differential to set S MCSI value)        In case of transmission mode 3: One RI value        
Reporting Mode 3-1
Contents of this report for transmission modes 1-8:                One set S MCSI value per codeword        One preferred PMI for set S        One MCSI value per codeword per subband (2 bits differential to set S MCSI value)        In case of transmission modes 4 or 8: One RI value        
Contents of this report for transmission mode 9:                One set S MCSI value per codeword        One first preferred PMI for set S        One second preferred PMI for set S        One MCSI value per codeword per subband (2 bits differential to set S MCSI value)        One RI value        
The below Table 1 discloses the amount of bits used for CSI reporting for the different Transmission Modes and Reporting Modes combinations. Whether or not the RI value is transmitted as well, is not considered in the following Table 1, i.e. the bits only cover the CSI reporting as such, MCSI (CQI) and PMI. It should be noted that for some modes detailed numbers are not yet agreed in the standard, and may thus be changed during further standardization. However, this will not have a significant impact on the invention that will be presented later on.
As mentioned above, for this table it is assumed that the component carrier has a 20 MHz bandwidth.
TABLE 1Antenna port& rank indicatorReporting ModeTransmission Mode #conditions1-22-03-02-23-11NANA2430NANA(Single-antenna port 0)7(if the number of PBCHantenna ports is one, single-antenna port, port; otherwisetransmit diversity)22TX or 4TXNA2430NANA(Transmit diversity)antenna ports32TX antenna portsNA2430NANA(Transmit Diversity if the4TX antenna ports2430associated rank indicator is1, otherwise large delayCDD)42TX antenna ports RI = 130NANA2832(Closed-loop spatial2TX antenna ports RI > 1213261multiplexing)4TX antenna ports RI = 15632344TX antenna ports RI > 160386452TX antenna portsNANANANA32(Multi-user MIMO)4TX antenna ports3462TX antenna ports30NANA2832(Closed-loop spatial4TX antenna ports563234multiplexing with singletransmission layer)82TX antenna ports RI = 130243028322TX antenna ports RI > 12132614TX antenna ports RI = 15632344TX antenna ports RI > 160386492TX antenna ports RI = 134NANA36362TX antenna ports RI > 12540654TX antenna ports RI = 16140384TX antenna ports RI > 1644668
For instance, in transmission mode 1 and reporting mode 3-0, the CQI reporting includes 30 bits of information. In the assumed 20 Mhz component carrier scenario, for mode 3-0 there would be 13 subbands in total (100 resource blocks in total, with 8 resource blocks per subband). For each subband a differential MCSI with 2 bits is reported back. In addition, there is a wideband MCSI with 4 bits (assuming aperiodic reporting of the CSI). Therefore, the CSI feedback is composed of 30 bits.
It should be noted that the term subband is here used so as to represent a number of resource blocks as outlined earlier, while the term set S represents generally a subset of the whole set of resource blocks in the system bandwidth. In the context of 3GPP LTE and LTE-A, the set S so far is defined to always represent the whole cell, i.e. component carrier bandwidth, a frequency range of up to 20 MHz, and is for simplicity hereafter referred to as “wideband”. However, in the future the set S may as well only refer some of the resource blocks of the cell, in which case the skilled person shall pay attention to interpret the term wideband (or set S) used in connection with the embodiments of the invention broader than only “wideband” (or “set S) as such.
Aperiodic & Periodic CQI Reporting
The periodicity and frequency resolution to be used by a UE to report on the CSI are both controlled by the eNodeB. The Physical Uplink Control Channel (PUCCH) is used for periodic CSI reporting only; the PUSCH is used for aperiodic reporting of the CSI, whereby the eNodeB specifically instructs the UE to send an individual CSI report embedded into a resource which is scheduled for uplink data transmission.
In addition, in case of multiple transmit antennas at the eNodeB, CSI values(s) may be reported for a second codeword. For some downlink transmission modes, additional feedback signaling consisting of Precoding Matrix Indicators (PMI) and Rank Indications (RI) is also transmitted by the UE.
In order to acquire CSI information quickly, eNodeB can schedule aperiodic CSI by setting a CSI request bit in an uplink resource grant sent on the Physical Downlink Control Channel.
In 3GPP LTE, a simple mechanism is foreseen to trigger the so-called aperiodic channel quality feedback from the user equipment. An eNodeB in the radio access network sends a L1/L2 control signal to the user equipment to request the transmission of the so-called aperiodic CSI report (see 3GPP TS 36.212, section 5.3.3.1.1 and 3GPP TS 36.213, section 7.2.1 for details). Another possibility to trigger the provision of aperiodic channel quality feedback by the user equipments is linked to the random access procedure (see 3GPP TS 36.213, section 6.2).
Whenever a trigger for providing channel quality feedback is received by the user equipment, the user equipment subsequently transmits the channel quality feedback to the eNodeB. Commonly, the channel quality feedback (i.e. the CSI report) is multiplexed with uplink (user) data on the Physical Uplink Shared CHannel (PUSCH) resources that have been assigned to the user equipment by L1/L2 signalling by the scheduler (eNodeB). In case of carrier aggregation, the CSI report is multiplexed on those PUSCH resources that have been granted by the L1/L2 signal (i.e. the PDCCH) which triggered the channel quality feedback.
Mismatch About Component Carrier Activation Status
It is important that the eNodeB and the UE have the same understanding about which component carriers are activated and which are deactivated. Since the channel state information feedback is multiplexed with data on the PUSCH channel, care must be taken that the user equipment and the eNodeB have the same understanding about which part of an uplink transmission on the PUSCH within a sub-frame is the channel quality feedback and which part is the user data. As apparent from FIG. 5, since the size of the channel state information is variable (depending on the number of activated component carriers, reporting mode, transmission mode etc., see Table 1), the remaining data size is also variable.
If the understanding is the same on both sides, there is no problem because the eNodeB configures the reporting mode and sets the aperiodic CQI trigger, so it knows when the UE transmits the feedback and also knows the size of the channel state information and—by specification—the location of the feedback and data part within the sub-frame so that the individual parts may be recovered.
However, the assumption by the eNodeB about the size of the channel quality feedback might not correspond to the actual size transmitted by the UE. A misunderstanding in said respect may lead to various disadvantages. Since the channel state information report is assumed by the eNodeB to include more or fewer information bits than it actually has, the eNodeB will not succeed in correctly decoding the channel state information, which might lead to an inefficient resource allocation or a renewed channel quality feedback request to recover.
Furthermore, on the other hand, due to the multiplexing of feedback and data part and a possible size misunderstanding, situations may occur where CSI bits are assumed to be data bits by the eNodeB, thus corrupting the data transmission, and in particular the PUSCH HARQ buffer to which the wrong data bits were provided without noticing.
Moreover, one channel state information report may be associated with the wrong component carrier. As can be seen from FIG. 6, the channel state information may comprise information on all component carriers CoCa#1-5. The CSI information is concatenated for the activated component carriers. Assuming that component carriers #1 and #4 are deactivated by the UE without the eNodeB noticing (because of discontinued reception, DRX, described later), a CSI report by the UE would include channel state information for only component carriers #2, 3 and 5, whereas the eNodeB expects channel state information for all five component carriers. The difference in understanding is illustrated in FIG. 7. The corresponding CSI feedback comprising three CSI reports for component carriers #2, 3 and 5 is illustrate in FIG. 8.
Accordingly, when receiving the feedback information from the UE, the eNodeB might associate the first channel state information with component carrier #1, instead of #2. Correspondingly, the eNodeB would interpret the second channel state information for component carrier #2, instead of component carrier #3, and interpret the third channel state information as being for component carrier #3, though it actually is for component carrier #5. In summary, the eNodeB would interpret the channel feedback information wrongly and make wrong assumption on the channel quality of the different component carriers. In addition, it would interpret data information as channel state information for the remaining component carriers #4 and #5 in this example, since it expects more channel state information data, than was actually transmitted by the UE.
According to another example, the eNodeB transmits a MAC control element including a bitmap that effectively activates one component carrier and deactivates another component carrier. In said case, even if the MAC control element gets lost on the way to the UE, the resulting channel state information transmitted by the UE would have the same size as the one expected by the eNodeB. However, the channel state information would also be associated wrongly to component carriers.
A misunderstanding of the activation status of component carriers between the UE and the eNodeB might be the result of different circumstances.
As described above, downlink component carriers are deactivated based on a deactivation timer, which is reset for every downlink transmission. For example, the user equipments are able to go into a DRX mode when it is not receiving any control signal for a defined number of sub-frames. Depending on the UE implementation there may be cases where the UE deactivates the component carrier when entering the DRX mode (though this is no necessarily the case, and is also not important to the functioning of the present invention). The eNodeB may send a control signal, but due to erroneous reception (e.g. as a result of noise on the channel, etc.) the user equipment is not aware of the control signal and may enter DRX mode and then deactivate the corresponding component carrier. The eNodeB however believes the component carrier of the user equipment still to be in an activated mode.
For 3GPP LTE-A where LTE carrier aggregation will be most likely used, it is possible that the user equipment goes into DRX mode per LTE carrier (component carrier). Assuming the above implementation of the DRX function, the UE can be in DRX mode for some component carriers available for communication, while it is still activated for other component carriers. Since the user equipment is not receiving or processing any signals from component carriers for which the user equipment is in DRX mode, it can be assumed that no CSI is usually measured and reported for such component carriers.
The problem for CSI reporting is that the user equipment is configured to only report channel quality elements for component carriers that are activated. Therefore, if the understanding on DRX mode for the component carriers is different between the user equipment and the eNodeB (i.e. different understanding on the activated/deactivated status), the user equipment and the eNodeB will have different understandings on the content of the channel quality feedback.
The downlink component carrier activation/deactivation is also implemented by using a corresponding MAC control element procedure, in which a bitmap is transmitted to the UE. The bitmap indicates the activation/deactivation status for all component carriers. The bitmap may be received with errors or with an unexpected delay, for example due to necessary re-transmissions. In any case, on the one hand it is not clear when exactly the UE will activate/deactivate a particular component carrier, since there might be a delay of several subframes. Furthermore, in case the bitmap is received in the UE with erroneous information, some component carriers will be wrongly activated/deactivated by the UE, and the eNodeB would not be aware of this.